The invention concerns a method for the manufacture of at least two-layered composite bodies having a support material completely or primarily comprising plastic and with a porous layer made from expanded polymer firmly attached thereto, in that a polymer treated with foaming agent is heated with microwave energy up to the melting temperature of the polymer with simultaneous decomposition or evaporation of the foaming agent, with the resulting expanded polymer being connected to the support material.
Composite bodies of the above mentioned kind have a plurality of practical applications, e.g. as heat and acoustic insulation materials in building construction and renovation, in motor vehicle chassis construction etceteras. To the extent that such composite bodies are utilized for base materials for the internal lining of motor vehicles, not only the acoustical insulation properties but, in particular, the cushioning properties of the porous layer are used for safety reasons. Another application is acoustical and heat insulation layering for machines, thermal insulation containers etceteras.
The support material and the expanded polymer are normally each manufactured separately in their desired shapes and then glued together. This is usually done using solvent to effect a surface etching of the support material and the expanded polymer leading to firm bonding. When glues are used, they normally also contain solvent. This procedure is complicated and the use of solvents causes processing and environmental problems.
WO92/08642 describes a method for the production of molded bodies from expandable polymer pellets using a microwave-absorbing medium, wherein the polymer pellets, together with the MW absorbing medium such as water, are introduced into a MW permeable mold with the mold then being closed and the polymer pellets expanded and melted together using MW energy. A variation of the method provides for the packaging of a molded body made in this manner using a liner introduced into the mold and surrounding the polymer pellets which, however, only effects an interlocking connection to the expanded polymer pellets.
A further method is described in EP 0 705 682 A1 for connecting at least two thermoplastic polymers, wherein at least one of the polymers is coated with an MW absorbing medium at least at the surface bordering the other polymer so that the polymers are welded together under contact at their bordering surfaces in a MW field by means of heat transfer from the MW absorbing medium.
It is the purpose of the present invention to propose a method for the manufacture of composite bodies of the above mentioned structure which can be carried out without the use of solvents, wherein addition of additives, such as MW absorbing media, is not necessary.